Method and system for wafer-level testing

ABSTRACT

The present disclosure provides a method and a system for testing semiconductor device. The method includes the following operations. A wafer having an IC formed thereon is provided. The IC is energized by raising the voltage of the IC to a first voltage level during a first period. A stress signal is applied to the IC. The stress signal includes a plurality of sequences during a second period subsequent to the first period. Each of the sequence has a ramp-up stage and a ramp-down stage. The stress signal causes the voltage of the IC to fluctuate between a second voltage level and a third voltage level. Whether the IC complies with a test criterion is determined after applying the stress signal.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims is a continuation of prior-filed U.S. application Ser. No. 16/522,551, filed Jul. 25, 2019, and claims the benefit of prior-filed provisional application No. 62/719,044, filed Aug. 16, 2018, under 35 U.S.C. 120.

BACKGROUND

In semiconductor fabrication, a wafer typically undergoes numerous processes to form an integrated circuit. Various wafer-level tests are performed to determine performance and reliability of the integrated circuit under various conditions and wafer acceptance. Wafer-level reliability testing is utilized for detecting potential for early failure associated with defects generated during fabrication of the integrated circuit. Generally, reliability testing involves stressing the integrated circuit using various techniques such as on/off power cycling and applying voltages that exceed normal operating conditions. However, current testing techniques may provide invalid reliability assessment due to unexpected damage or degradation of the integrated circuit during testing, so a more effective stressing method for testing is a must.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It should be noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a diagrammatic view of a system for testing semiconductor device in accordance with some embodiments of the present disclosure.

FIG. 2A is an illustration of a multiple-step power signal for testing a wafer in accordance with some embodiments of the present disclosure.

FIG. 2B is an illustration of a multiple-step ramp-up and ramp-down stages of the sequence in accordance with some embodiments of the present disclosure.

FIG. 3A is an illustration of a single-step power signal for testing a wafer in the conventional dynamic voltage stress test method.

FIG. 3B is an illustration of a single-step power signal for testing a wafer in the conventional elevated voltage stress test method.

FIG. 4 is an illustration of a multiple-step power signal for testing a wafer in accordance with some embodiments of the present disclosure.

FIG. 5 is an illustration of a multiple-step power signal for testing a wafer in accordance with some embodiments of the present disclosure.

FIG. 6 is an illustration of a multiple-step power signal for testing a wafer in accordance with some embodiments of the present disclosure.

FIG. 7 is a flowchart illustrating a method in accordance with some embodiments of the present disclosure.

FIG. 8 is a flowchart illustrating a method in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Embodiments of the present disclosure are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative and do not limit the scope of the disclosure.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” “lower,” “left,” “right” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. It should be understood that when an element is referred to as being “connected to” or “coupled to” another element, it may be directly connected to or coupled to the other element, or intervening elements may be present.

In some conventional voltage stress tests, the screen rate (i.e., the fail count divided by the total device numbers) for wafer-level testing may need to be improved. It is discovered that rapidly changing the toggle state (i.e., “0” state or “1” state) of the semiconductor devices in the integrated circuit (IC) may improve the screen rate for wafer-level testing. According to some embodiments of the present disclosure, the signal generator may provide a cyclic alternating voltage stress (CAVS) that the stress signal having a plurality of sequences, which cause the voltage level to alternately fluctuate between a high voltage level and a low voltage level in a time period. The toggle state (i.e., “0” state or “1” state) of the semiconductor devices in the integrated circuit (IC) may be changed more easily by the CAVS during the multiple ramp-up and ramp-down stages. The reason is that the field effect is alternated locally. As a result, the stress signal may cause some of the semiconductor devices to become a short mode as a fail count. The swap rate of the semiconductor devices in the IC may be increased due to the multiple ramp-up and ramp-down stages. Thus, the screen rate for wafer-level testing may be improved.

FIG. 1 is a diagrammatic view of a system 100 for testing semiconductor device in accordance with some embodiments of the present disclosure. FIG. 2A is an illustration of a multiple-step power signal for testing a wafer in accordance with some embodiments of the present disclosure. Referring to FIG. 1 and FIG. 2A, the system 100 is configured to test an integrated circuit (IC) formed on a wafer 110. The wafer 110 may be referred to as a device under test (DUT). The wafer 110 may comprise an elementary semiconductor such as silicon, germanium, or diamond. The wafer 110 may include one or more ICs 112 (or chips) formed thereon. Scribe lines may be provided between adjacent ICs 112 so that the ICs can be separated in subsequent processing.

In some embodiments, the system 100 may be automatic test equipment (ATE). The system 100 may include hardware and software components that provide a suitable operational and functional environment for the tests. In some embodiments, the system 100 includes a signal generator 102, a coupler 104 and a module 106.

The signal generator 102 is configured to generate a cyclic alternating voltage stress (CAVS). The CAVS includes a signal of a first voltage level 200 during a first period 210 and a stress signal 220 during a second period 212 subsequent to the first period 210. It should be understood that other electrical signals such as data signals and clock signals may be provided to the DUT but are not illustrated for the sake of clarity and simplicity.

In some embodiments, during the first period 210, a single-step signal that rises from ground (i.e., 0 V) to a first voltage level 200 is generated. The first voltage level 200 may be the nominal voltage of the IC 112. The IC 112 may be energized with the nominal voltage for a power cycling test. In some embodiments, the duration of rising from ground to the first voltage level 200 may be about 6-10 milliseconds (ms).

In some embodiments, during the second period 212, the stress signal 220 is generated. The stress signal 220 functions to overstress the DUT and induce failures associated with the fabrication process. The stress signal 220 may include a plurality of sequences 221A and 221B. Each of the sequences 221A and 221B includes a ramp-up stage 2231 and a ramp-down stage 2232. Each of the sequences 221A and 221B includes a change in voltage between a second voltage level 222 and a third voltage level 224. A range of the ramp-up stage 2231 or the ramp-down stage 2232 is not limited. In some embodiments, the range of the ramp-up stage 2231 or the ramp-down stage 2232 is between about 0.1 V/millisecond (ms) and about 0.3 V/ms. The ramp-up stage 2231 raises the voltage from the first voltage level 200 to the second voltage level 222, and the ramp-down stage 2232 decreases the voltage from the second voltage level 222 to the third voltage level 224.

It should be understood that the stress signal may vary depending on test requirements and/or historical data. For examples, the stress signal may depend on the defect parts-per-million (DPPM). In some industries, the defect tolerance may be lower, e.g. automobile or mobile phone industry, the sequences of the stress signal may be increased. The second voltage level 222 is higher than the first voltage level 200. The value of the second voltage level 222 is not limited. In some embodiments, the second voltage level 222 may be about 1.3 to about 2.0 times the first voltage level 200. The second voltage level 222 serves as a test voltage (or stress voltage). The value of the third voltage level 224 is not limited. The third voltage level 224 may be equal to or lower than the first voltage level 200. In some embodiment, a voltage difference between the second voltage level 222 and the third voltage level 224 is greater than a voltage difference between the first voltage level 200 and the second voltage level 222. A duration of the third voltage level 224 may include a waiting time and a check alarm time. The duration of the third voltage level 224 is not limited. In some embodiments, the duration of the third voltage level 224 may be about 6-10 ms.

FIG. 2B is an illustration of a multiple-step ramp-up and ramp-down stages of the sequence in accordance with some embodiments of the present disclosure. Referring to FIG. 2B, in some embodiments, the ramp-up stage 2231′ and the ramp-down stage 2232′ includes multiple steps. With multiple steps, the current overshoot may be avoided. It should be noted that the number of steps of the ramp-up stage 2231′ and the ramp-down stage 2232′ are not limited.

Referring back to FIG. 1 and FIG. 2A, the coupler 104 is configured to couple the signal generator 102 to the IC 112. In some embodiments, the coupler 104 may be coupled to the IC by a plurality of probes 101. The probes 101 may be part of a probe head or probe package (not shown). The probes 101 may be electrically coupled to test pads and/or bonding pads disposed on the ICs 112. The test pads and/or bonding pads provide electrical connections to an interconnect structure (e.g., wiring) of the ICs. For example, some of the probes may be coupled to pads that are associated with a supply terminal (e.g., Vdd) and ground terminal (e.g., Vss) of the IC 112. Other probes may be coupled to pads associated with input/output (I/O) terminals (e.g., data signals) of the IC 112. As such, the system 100 is operable to apply electrical signals (e.g., stress signal) to the IC 112 and obtain response signals from the IC 112 during wafer-level testing.

The module 106 is configured to determine whether the IC 112 complies with a test criterion after the stress signal 220 is applied to the IC 112. The response signals may be evaluated by the module 106 with respect to the test criterion to determine whether a particular IC 112 is defective or not.

FIG. 3A is an illustration of a single-step power signal for testing a wafer in an existing dynamic voltage stress test method. FIG. 3B is an illustration of a single-step power signal for testing a wafer in an existing elevated voltage stress test method.

Referring to FIG. 3A, a stress signal 312 of the dynamic voltage stress (DVS) test is applied in a single test period 310. The stress signal 312 is composed of a single-sequence signal, which includes a ramp-up stage rising from ground 313 to a test voltage 311, and a ramp-down stage lowering from the test voltage 311 to ground 313. The DVS test utilizes the single-sequence signal to power on the DUT to the pattern setup status and test the DUT at the test voltage 311 the same time period. The test voltage 311 exceeds the normal operating voltages during the test period 310. In the DVS test, it is found that if the voltage level of the test voltage 311 is raised, the screen rate (i.e., the fail count divided by the total device number) for wafer-level testing may be increased. However, the test voltage 311 is used both for pattern setup and defect test at the same time, and the quantity of voltage change of the test voltage 311 is thus limited due to the requirement for pattern setup. In other words, the test voltage 311 may not be able to be increased because of the requirement for pattern setup. Therefore, the screen rate of the DVS test is limited.

To mitigate the problems of the DVS test, the EVS test was introduced. Referring to FIG. 3B, in the EVS test, a stress signal 328 includes a single-step signal 321 and a single-sequence signal 324, which are applied in a first period 320 and a second period 322, respectively. In the first period 320, the single-step signal 321 that rises from ground 323 to a normal operating voltage 325 is applied. In the second period 322 immediately following the first period 320, the single-sequence signal 324 that rises from the normal operating voltage 325 to a test voltage 327 is applied. In the EVS test, it is found that instead of increasing the voltage level of the test voltage 327, the screen rate for wafer-level testing may be increased by increasing the duration of the test voltage 327 during the second period 322. However, in order to obtain a higher screen rate, the second period 322 may be much longer than the test period 310 (shown in FIG. 3A) of the DVS test. For example, the second period 322 of the EVS test may be ten times longer than the test period 310 of the DVS test. Moreover, the screen rate of the EVS test may only be equal to or even less desirable than the DVS test.

The concerns mentioned above may be alleviated according to the present disclosure.

According to some embodiments of the present disclosure, instead of increasing the voltage level or the time period of the test voltage, the screen rate for wafer-level testing may be increased by increasing the quantity of voltage changes in the stress signal 220. Referring back to FIG. 1 and FIG. 2A, in some embodiments of the present disclosure, the signal generator 102 provides the CAVS that the stress signal 220 with the plurality of sequences 221A and 221B, which cause the voltage level to fluctuate between the second voltage level 222 and the third voltage level 224 in the second period 212. Accordingly, the wafer 110 undergoes multiple iterations of voltage change during the second period 212.

As described above, for example, the stress signal 220 includes two sequences 221A and 221B, wherein each sequence 221A and 221B includes the ramp-up stage 2231 and the ramp-down stage 2232. In some embodiments, the signal generator 102 provides the sequence 221A to energize the IC 112 by increasing the voltage of the IC 112 from the first voltage level 200 (i.e., the nominal voltage of the IC) to the second voltage level 222 (i.e., the test voltage). When the ramp-up stage 2231 is applied, a state (i.e., “0” state or “1” state) of at least one semiconductor device in the IC 112 may be changed or toggled. Next, the signal generator 102 continues the sequence 221A to energize the IC 112 by decreasing the voltage subsequent to the ramp-up stage 2231. The ramp-down stage 2232 decreases the voltage of the IC 112 from the second voltage level 222 to the third voltage level 224. When the ramp-down stage 2232 is applied, the state of at least one semiconductor device in the IC 112 may be changed or toggled.

After the sequence 221A, the signal generator 102 provides the sequence 221B to energize the IC 112. The signal generator 102 provides the sequence 221B to energize the IC 112 by increasing the voltage of the IC 112 from the third voltage level 224 to the second voltage level 222. Next, the signal generator 102 continues the sequence 221B to energize the IC 112 by decreasing the voltage of the IC 112 from the second voltage level 222 to ground or the first voltage level 200. As with the sequence 221A, the state of the semiconductor device in the IC 112 may be changed or toggled by the ramp-up stage 2231 and the ramp-down stage 2232 during the sequence 221B.

In summary, according to some embodiments of the present disclosure, during the second period 212, the stress signal 220 may include a plurality of ramp-up stages 2231 and ramp-down stages 2232. It is discovered that the state of the semiconductor devices in the IC 112 may be changed or toggled more easily by the CAVS during the ramp-up stages 2231 and the ramp-down stages 2232. The reason is that the field effect is alternated locally. As a result, the voltage difference of the ramp-up stage 2231 and the ramp-down stages 2232 may cause some of the semiconductor devices in the IC 112 to become a short mode as a fail count. The swap rate of the semiconductor devices in the IC 112 may be increased due to the multiple ramp-up and ramp-down stages. Thus, the screen rate for wafer-level testing may be increased with the plurality of sequences 221A and 221B causing fluctuation of the voltage of the IC 112 between the second voltage level 222 and the third voltage level 224.

Moreover, according to some embodiments of the present disclosure, the swap rate of the semiconductor devices in the IC 112 may be further increased by increasing the amount of the ramp-up stage 2231 from the first voltage level 200 to the second voltage level 222, or by increasing the amount of the ramp-down voltage 2232 from the second voltage level 222 to the third voltage level 224. In other words, the screen rate for wafer-level testing may further be increased by increasing the change in voltage that occurs during the ramp-up stage 2231 or during the ramp-down stage 2232. It should be understood that in order to increase swap rate, any test algorithm that would cover 0/1 state combination is not limited. For example, MBIST (Memory built-in self-test) test may use one CKB (checkerboard) and one inverse CKB test pattern. Logic test pattern may consider a combination of several chain test.

Compared to the DVS test, the test of the present disclosure provides increased screen rate due to larger voltage differences during the ramp-up stage 2231 and the ramp-down stage 2232. In the present disclosure, the test voltage 222 is separated from the pattern setup voltage (i.e., the first voltage level 200). Thus, the test voltage 222 in the present disclosure may be higher than the test voltage 311 (shown in FIG. 3A) of the DVS test. Therefore, the screen rate may be increased.

Compared to the EVS test, since the multiple ramp-up and ramp-down stages of the present disclosure may increase the swap rate of the semiconductor devices in the IC 112, the extended period 322 (shown in FIG. 3B) may be reduced in the present disclosure. Therefore, the duration of the second period 212 in the present disclosure can be reduced and the time consuming concern in the conventional EVS test may be alleviated.

It should be noted that the application of the CAVS is not a limitation of the present disclosure. In some embodiments, the CAVS may be applied in chip probing flow, final test flow, or wafer acceptance test flow at room temperature range (about 25° C. to about 27° C.), or temperature range from about 0° C. to about −40° C., or temperature range from 0° C. to about 125° C.

FIG. 4 is an illustration of a multiple-step power signal for testing a wafer in accordance with some embodiments of the present disclosure. The signal generator 102 (shown in FIG. 1 ) is configured to generate the CAVS including a stress signal 420 during a second period 412 subsequent to the first period 210. The first period 210 is described in FIG. 2A and is omitted here for brevity.

In some embodiments, during the second period 412, the stress signal 420 is generated. The stress signal 420 may include a plurality of sequences 421A, 421B, 421C and 421D. Each sequence 421A, 421B, 421C and 421D includes a ramp-up stage 4231 and a ramp-down stage 4232. Each sequence 421A, 421B, 421C and 421D fluctuates between the second voltage level 422 and the third voltage level 424. A range of the ramp-up stage 4231 or the ramp-down stage 4232 is not limited. In some embodiments, a range of the ramp-up stage 4231 or the ramp-down stage 4232 is between about 0.1 V/ms and about 0.3 V/ms. The voltage is increased from the first voltage level 200 to the second voltage level 422, then decreased from the second voltage level 422 to the third voltage level 424, then increased from the third voltage level 424 to the second voltage level 422, and finally decreased from the second voltage level 422 to the first voltage level 200. It should be noted the second voltage level 422 and the third voltage level 424 may be the same as the second voltage level 222 and the third voltage level 224, respectively, in FIG. 2A.

The second voltage level 422 is higher than the first voltage level 200. The value of the second voltage level 422 is not limited. In some embodiments, the second voltage level 422 may be 1.3 to 2.0 times the first voltage level 200. The second voltage level 422 serves as the test voltage. The value of the third voltage level 424 is not limited. The third voltage level 424 may be equal to or less than the first voltage level 200. In some embodiments, a voltage difference between the second voltage level 422 and the third voltage level 424 is greater than a voltage difference between the first voltage level 200 and the second voltage level 422.

As described above, according to some embodiments of the present disclosure, the screen rate for wafer-level testing may be increased by increasing the quantity of the voltage changes in the stress signal 420. In some embodiments, the signal generator 102 may provide the stress signal 420 with the plurality of sequences 421A, 421B, 421C and 421D fluctuating between the second voltage level 422 and the third voltage level 424 during the second period 412.

As an example, the stress signal 420 includes four sequences 421A, 421B, 421C and 421D and each sequence 421A, 421B, 421C and 421D includes an ramp-up stage 4231 and a ramp-down stage 4232. In some embodiments, the signal generator 102 provides the sequence 421A to energize the IC 112 (shown in FIG. 1 ) by increasing the voltage of the IC 112 from the first voltage level 200 to the second voltage level 422. When the ramp-up stage 4231 is applied, a state of at least one semiconductor device in the IC 112 may be changed or toggled. Next, the signal generator 102 continues the sequence 421A to energize the IC 112 by decreasing the voltage subsequent to the ramp-up stage 4231. The voltage of the IC 112 is decreased from the second voltage level 422 to the third voltage level 424. When the ramp-down stage 4232 is applied, the state of at least one semiconductor device in the IC 112 may be changed or toggled.

After the sequence 421A, the signal generator 102 provides the sequence 421B to energize the IC 112. The signal generator 102 provides the sequence 421B to energize the IC 112 by increasing the voltage of the IC 112 from the third voltage level 424 to the second voltage level 422. Next, the signal generator 102 continues the sequence 421B to energize the IC 112 by decreasing the voltage of the IC 112 from the second voltage level 422 to the third voltage level 424. As with the sequence 421A, the state of the semiconductor device in the IC 112 may be changed or toggled by the ramp-up stage 4231 and the ramp-down stage 4232 during the sequence 421B. It should be understood that the ramp-down stage 4232 of the sequence 421B may decrease the voltage of the IC 112 from the second voltage level 422 to another voltage lower than the third voltage level 424. After the sequence 421B, the signal generator 102 provides the sequence 421C to energize the IC 112 in a similar manner, and the description thereof is omitted here for brevity.

After the sequence 421C, the signal generator 102 provides the sequence 421D to energize the IC 112. The signal generator 102 provides the sequence 421D to energize the IC 112 by increasing the voltage of the IC 112 from the third voltage level 424 to the second voltage level 422. Next, the signal generator 102 continues the sequence 421D to energize the IC 112 by decreasing the voltage of the IC 112 from the second voltage level 422 to ground or the first voltage level 200. As with the sequences 421A and 421B, the state of the semiconductor device in the IC 112 may be changed or toggled by the ramp-up stage 4231 and the ramp-down stage 4232 during the sequence 421D.

In summary, according to some embodiments of the present disclosure, during the second period 412, the stress signal 420 may include a plurality of ramp-up stages 4231 and ramp-down stages 4232. It is discovered that the state of the semiconductor devices in the IC 112 may be changed or toggled more easily by the CAVS during the ramp-up stages 4231 and the ramp-down stages 4232. The reason is that the field effect is alternated locally. As a result, the voltage difference of the ramp-up stage 4231 and the ramp-down stages 4232 may cause some of the semiconductor devices in the IC 112 to become a short mode as a fail count. By using the present CAVS, the swap rate of the semiconductor devices in the IC 112 may be increased due to the multiple ramp-up and ramp-down stages. Thus, the screen rate for wafer-level testing may be increased with the plurality of sequences 421A, 421B, 421C and 421D causing fluctuation of the voltage of the IC 112 between the second voltage level 422 and the third voltage level 424. It should be noted that the CAVS may have higher defect coverage on short mode failure but is not limited to only cover short mode failure.

Moreover, according to some embodiments of the present disclosure, the swap rate of the semiconductor devices in the IC 112 may be further increased by increasing the amount of the ramp-up stage 4231 from the first voltage level 200 to the second voltage level 422, or by increasing the amount of the ramp-down voltage 2232 from the second voltage level 422 to the third voltage level 424. In other words, the screen rate for wafer-level testing may further be increased by increasing the change in voltage that occurs during the ramp-up stage 4231 or during the ramp-down stage 4232.

FIG. 5 is an illustration of a multiple-step power signal for testing a wafer in accordance with some embodiments of the present disclosure. The signal generator 102 (shown in FIG. 1 ) is configured to generate a stress signal 520 during a second period 512 subsequent to the first period 210. The first period 210 is described in FIG. 2A and is omitted here for brevity.

The difference between the stress signal 520 and the stress signal 220 in FIG. 2A is that the stress signal 520 may have longer duration at second voltage level 522 comparing to the stress signal 220. The stress signal 520 may have a sequence 521A with longer duration at second voltage level 522 and a sequence 521B with shorter duration at second voltage level 522. It should be noted that stress signal 520 may have more than one sequence 521B with shorter duration at second voltage level 522. In some embodiments, the duration of the sequence 521B is similar to the duration of the sequences 221A, 221B in FIG. 2A.

FIG. 6 is an illustration of a multiple-step power signal for testing a wafer in accordance with some embodiments of the present disclosure. The signal generator 102 (shown in FIG. 1 ) is configured to generate a signal of a first voltage level 600 during a first period 610 and a stress signal 620 during a second period 612 subsequent to the first period 610. The stress signal 620 may include a plurality of sequences 621A, 621B and 621C. The sequences 621A, 621B and 621C are similar to the sequences 421A, 421B and 421D in FIG. 4 and here are omitted for brevity.

The difference between the signal in FIG. 6 and the signal in FIG. 2A is that the first voltage level 600 is higher than the first voltage 200. The value of the first voltage level 600 is not limited. In some embodiments, the first voltage level 600 may be about 1.1 to about 1.3 times the first voltage level 200.

FIG. 7 is a flowchart illustrating a method in accordance with some embodiments of the present disclosure. The method 700 of wafer-level testing may include operations 712, 714, 716 and 718. In operation 712, a wafer having an IC formed thereon is provided. In operation 714, the IC is energized by raising the voltage of the IC to a first voltage level during a first period. In operation 716, a stress signal is applied to the IC. The stress signal includes a sequence of multiple ramp-up stages and ramp-down stages during a second period subsequent to the first period. The sequences cause the voltage of the IC to fluctuate between a second voltage level and a third voltage level. In operation 718, it is determined whether the IC complies with a test criterion after applying the stress signal. The detailed descriptions of such operations are similar to the descriptions of the operations shown in FIG. 1 , FIG. 2A, and FIG. 4 , and thus are omitted for brevity.

FIG. 8 is a flowchart illustrating a method in accordance with some embodiments of the present disclosure. The method 800 of wafer-level testing may include operations 812, 814, 816 and 818. In operation 812, a wafer having an IC formed thereon is provided. In operation 814, the IC is energized by raising the voltage of the IC to a first voltage level during a first period. In operation 816, a stress signal is applied to the IC. The stress signal includes a plurality of ramp-up stages and a plurality of ramp-down stages during a second period subsequent to the first period. The ramp-up stages and the ramp-down stages are applied alternately. In operation 818, it is determined whether the IC complies with a test criterion after applying the stress signal. The detailed descriptions of such operations are similar to the descriptions of the operations shown in FIG. 1 , FIG. 2A, and FIG. 4 , and thus are omitted for brevity.

In summary, according to some embodiments of the present disclosure, the toggle state (i.e., “0” state or “1” state) of the semiconductor devices in the IC may be changed or toggled more easily by the CAVS during multiple ramp-up and ramp-down stages. The reason is that the field effect is alternated locally. As a result, the voltage difference of the ramp-up stage and the ramp-down stages may cause some of the semiconductor devices in the IC to become a short mode as a fail count. By using the present CAVS, the swap rate of the semiconductor devices in the IC may be increased due to the multiple ramp-up and ramp-down stages. Thus, the screen rate (i.e., the fail count divided by the total device number) for wafer-level testing may be increased. Furthermore, according to some embodiments of the present disclosure, the screen rate for wafer-level testing may be further increased with greater voltage differences of the ramp-up stage or the ramp-down stage.

According to some embodiments, a method is provided. The method of wafer-level testing includes the following operations. A wafer having an IC formed thereon is provided. The IC is energized by raising the voltage of the IC to a first voltage level during a first period. A stress signal is applied to the IC. The stress signal includes a plurality of sequences during a second period subsequent to the first period. Each of the sequence has a ramp-up stage and a ramp-down stage. The stress signal causes the voltage of the IC to fluctuate between a second voltage level and a third voltage level. After applying the stress signal, it is determined whether the IC complies with a test criterion.

According to other embodiments, a method is provided. The method of wafer-level testing includes the following operations. A wafer having an IC formed thereon is provided. The IC is energized by raising the voltage of the IC to a first voltage level during a first period. A stress signal is applied to the IC. The stress signal includes a plurality of ramp-up stages and a plurality of ramp-down stages during a second period subsequent to the first period. The ramp-up stages and the ramp-down stages are applied alternately. After applying the stress signal, it is determined whether the IC complies with a test criterion.

According to other embodiments, a system for semiconductor device testing is provided. The system for semiconductor device testing includes a signal generator, a coupler and a module. The signal generator is configured to generate a first voltage level during a first period and a stress signal during a second period subsequent to the first period. The stress signal includes a plurality of sequences during a second period subsequent to the first period. Each of the sequence has a ramp-up stage and a ramp-down stage. The stress signal causes the voltage of the IC to fluctuate between a second voltage level and a third voltage level. The coupler is configured to couple the signal generator to an IC formed on a wafer. The module is configured to determine whether the IC complies with a test criterion after the stress signal is applied to the IC.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method, comprising: energizing an integrated circuit (IC) on a wafer by raising a voltage of the IC to a first voltage level during a first period; and applying to the IC a stress signal including a plurality of sequences during a second period subsequent to the first period, each of the sequence having a ramp-up stage and a ramp-down stage, wherein the stress signal causes the voltage of the IC to fluctuate between a second voltage level and a third voltage level, wherein a difference between the second voltage level and the third voltage level is greater than a difference between the first voltage level and the second voltage level.
 2. The method of claim 1, wherein the ramp-up stage or the ramp-down stage has a range between 0.1 V/millisecond (ms) and 0.3 V/ms.
 3. The method of claim 1, wherein the second voltage level is 1.3 to 2.0 times the first voltage level.
 4. The method of claim 1, wherein the first period is between 6 milliseconds and 10 milliseconds.
 5. The method of claim 1, wherein the second voltage level is higher than the first voltage level and the third voltage level is lower than the first voltage level.
 6. The method of claim 1, wherein the applying to the IC the stress signal including the plurality of sequences during the second period subsequent to the first period comprises: energizing the IC by raising the voltage of the IC from the first voltage level to the second voltage level.
 7. The method of claim 6, wherein a state of at least one semiconductor device in the IC is changed by the ramp-up stage.
 8. The method of claim 1, wherein the applying to the IC the stress signal including the plurality of sequences during the second period subsequent to the first period comprises: energizing the IC by decreasing the voltage of the IC from the second voltage level to the third voltage level.
 9. The method of claim 8, wherein a state of at least one semiconductor device in the IC is changed by the ramp-down stage.
 10. The method of claim 8, further comprising: energizing the IC by raising the voltage of the IC from the third voltage level to the second voltage level.
 11. A method, comprising: energizing an integrated circuit (IC) on a wafer by raising a voltage of the IC to a first voltage level during a first period; and applying to the IC a stress signal including a plurality of ramp-up stages and a plurality of ramp-down stages during a second period subsequent to the first period, wherein the ramp-up stage and the ramp-down stage are applied alternately; and wherein the second voltage level is higher than the first voltage level and the third voltage level is lower than the first voltage level.
 12. The method of claim 11, wherein the ramp-up stage or the ramp-down stage has a range between 0.1 V/millisecond (ms) and 0.3 V/ms.
 13. The method of claim 11, wherein the second voltage level is 1.3 to 2.0 times the first voltage level.
 14. The method of claim 11, wherein the applying to the IC the stress signal including the plurality of sequences during the second period subsequent to the first period comprises: energizing the IC by raising the voltage of the IC from the first voltage level to the second voltage level.
 15. The method of claim 14, wherein a state of at least one semiconductor device in the IC is changed by the ramp-up stage.
 16. A system for testing semiconductor device, comprising: a signal generator, configured to generate a first voltage level during a first period and a stress signal during a second period subsequent to the first period, the stress signal including a plurality of sequences during the second period subsequent to the first period, each of the sequence having a ramp-up stage and a ramp-down stage, wherein the stress signal causes the voltage of the IC to fluctuate between a second voltage level and a third voltage level; wherein a difference between the second voltage level and the third voltage level is greater than a difference between the first voltage level and the second voltage level.
 17. The system of claim 16, wherein the ramp-up stage or the ramp-down stage has a range between 0.1 V/millisecond (ms) and 0.3 V/ms.
 18. The system of claim 16, wherein the second voltage level is 1.3 to 2.0 times the first voltage level.
 19. The system of claim 16, wherein the second voltage level is higher than the first voltage level and the third voltage level is lower than the first voltage level.
 20. The system of claim 16, wherein the first period is between 6 milliseconds and 10 milliseconds. 